Soil is far more than dirt beneath our feet. It is a living system formed through the interaction of rock, climate, organisms, and time. Soil supports plant growth, stores water and nutrients, and plays a vital role in shaping landscapes and ecosystems across the Earth.
What Is Soil?
Soil is a mixture of: • Mineral particles from weathered rock • Organic matter from decaying plants and animals • Air and water • Living organisms such as bacteria, fungi, and insects
Together, these components create a dynamic environment where life can thrive.
How Soil Forms
Soil forms slowly through a process known as weathering, where rocks are broken down into smaller particles.
This happens through the 3 types of weathering: • Physical weathering (freeze–thaw, temperature change) • Chemical weathering (rainwater, acids) • Biological weathering (plant roots, organisms)
Over time, these particles mix with organic material to form soil.
Soil Horizons (Layers of Soil)
Most soils develop into layers called horizons:
• O Horizon – organic material such as leaf litter • A Horizon (Topsoil) – rich in nutrients and life • B Horizon (Subsoil) – minerals washed down from above • C Horizon – weathered rock fragments • Bedrock – solid rock beneath the soil
Soil and Living Organisms
Soil is alive.
A single handful of soil can contain: • Millions of bacteria • Fungi and mycorrhizal networks • Insects and worms
These organisms break down organic matter and recycle nutrients, making soil fertile and productive.
Soil and Landscape Change
Soil is constantly shaped by: • Erosion • Deposition • Climate • Human activity
Rivers, glaciers, wind, and farming can remove, transport, or enrich soil, altering landscapes over time.
Soil and Plants
Plants rely on soil for: • Anchoring roots • Water supply • Nutrients
Some plants, such as lupins, actively improve soil by adding nutrients and supporting ecological succession. These pioneer plants help landscapes recover after disturbance.
Why Soil Matters
Soil matters because it: • Supports nearly all life on land • Connects geology, biology, and climate • Records environmental change over time
Without healthy soil, ecosystems collapse, agriculture fails, and landscapes degrade.
Soil as a Record of the Past
Soil preserves clues about: • Past climates • Vegetation • Human activity
In this way, soil acts as a natural archive, storing evidence of Earth’s changing history beneath the surface.
